This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. In what has been called the world?s worst mass poisoning, between 35 and 70 million people are affected by chronic low-level arsenic poisoning in Bangladesh and surrounding areas. We have previously suggested that this poisoning is not directly due to the toxic effects of arsenic, but is instead primarily due to arsenic-induced selenium deficiency. We plan to build on our earlier work to provide a molecular foundation for the treatment of chronic low-level arsenic poisoning in Bangladesh and other affected areas. X-ray absorption spectroscopy (XAS) holds the key to these discoveries.